Benno van Dalen

Dutch historian of science with special interest in Islamic astronomy and its transmission between Islam and China, India and Europe.
Research leader in the project Ptolemaeus Arabus et Latinus at the Bavarian Academy of Sciences and Humanities in Munich.
Former editor of
Historia Mathematica, International journal of history of mathematics (2003-2009).

Research Interests

GENERAL RESEARCH INTERESTS: Ancient and medieval astronomical tables and methods of computation. Transmission of astronomical knowledge from the Islamic world to China, India and Europe.


Since 1 May 2013, I am employed at the Bavarian Academy of Sciences and Humanities in Munich. Together with Dr. David Juste, I am research leader of the new 25-year project Ptolemaeus Arabus et Latinus (project leader: Prof. Dr. Dag Nikolaus Hasse, University of Wrzburg; responsible advisory commission (“Beirat”): History of Science, chaired by Prof. Dr. Menso Folkerts). Main purpose of this project is to make available reproductions, transcriptions and finally editions of Ptolemy's surviving astronomical and astrological works (including pseudepigrapha) in Arabic and Latin translation. Also further important works from the medieval Ptolemaic tradition will be published and studied, including, among others, commentaries on Ptolemy's works, zjes and other works heavily influenced by Ptolemy. Brief general information on Ptolemaeus Arabus et Latinus, an overview of all team members, databases of Arabic and Latin Ptolemaic works and their manuscripts with scans of representative works as well as a Greek-Arabic-Latin glossary of astronomical and astrological terminology are available at our website, which is constantly further developed.


As part of the project Ptolemaeus Arabus et Latinus, I continue to work on a revised Survey Of Islamic Astronomical Tables. The original monograph with this title was published by E.S. Kennedy in 1956 (Transactions of the American Philosophical Society N.S. 46-2, reprinted in 1989) and included brief descriptions of little more than 100 Islamic astronomical handbooks with tables (so-called zjes), extensive abstracts of twelve of these, a classification of the subjects dealt with, and preliminary conclusions concerning the relations between, and the developments in the production of, Islamic astronomical handbooks. Nowadays, around 250 zjes are known, of which nearly 150 are extant in more or less complete form, but only very few have been published or investigated in detail.

The New Zj Survey will include at least the following:

At the moment around 130 entries of zjes for the New Zj Survey are basically ready. They involve investigations of a large number of works that until now have not yet been studied at all and hence provide the first descriptions of the contents of these works.


On the side, I hope to publish my investigation of the achievements of the Muslim astronomers who were brought to China by the Mongols in the early Yuan Dynasty (ca. 1270). The available sources for this investigation are:

  1. The Huihui lifa (c. 1383), a Chinese translation of a presumably Persian astronomical handbook with tables (a so-called zj), known to have been available in China in the beginning of the Yuan. TheHuihui lifa is extant in a number of somewhat different versions, apparently all deriving from a restoration of the original translation carried out by an officer of the Astronomical Bureau of the Ming dynasty in 1477.
  2. The Sanjufn Zj, an Arabic astronomical handbook written for the Mongol viceroy of Tibet in 1366.
  3. An Arabic or Persian manuscript at the Pulkovo Observatory (near St. Petersburg in Russia), which was obtained in China in the 19th century and contains only a set of astronomical tables.

Although the sources 1 and 2 are obviously two different works, a mathematical investigation of their planetary tables shows that they must be based on a common predecessor. It turns out that the two sources share values for most of the planetary parameters which are not found in any other Arabic or Persian astronomical handbooks (including those resulting from the extensive observational program at the contemporary Ilkhan observatory in Maragha). It is therefore probable that their common predecessor was a work compiled by the Muslim astronomers who were active at the official Islamic Observatory in the Chinese capital Beijing. The presence in one of the extant versions of the Huihui lifa of a large star table independent of Ptolemy's table in the Almagest also points to original, hitherto unknown Islamic observations.

According to a description published in 1882, the manuscript listed above as source no. 3 is very probably a partial copy of the original work on which both the Huihui lifa and the Sanjufn Zj are based. It was rediscovered in the early 2000s in the library of the Institute of Oriental Manuscripts of the Academy of Science in St. Petersburg.

At the moment I am working on an edition and English translation of, and extensive commentary on, the Chinese text of the Huihui lifa, which will be published as a monograph together with various results that have already been published separately in articles.


During my doctoral research (under the supervision of Prof. Dr. Henk Bos and Dr. Jan Hogendijk of the Mathematical Institute of Utrecht University, Netherlands) I concentrated on the development and application of statistical and numerical tools for the analysis of ancient and medieval astronomical tables. In a number of examples in my doctoral thesis Ancient and Mediaeval Astronomical Tables I used these tools to derive the mathematical structure and underlying parameters of a number of tables which had thus far defied explanation.

Furthermore, I wrote user-friendly computer programs for DOS-PC, by means of which various tasks frequently occurring in research on medieval astronomy can be conveniently carried out. These include: sexagesimal calculations (also with trigonometric functions); calendar conversions; input, analysis and output of trigonometric, spherical-astronomical, and (pseudo-linear) mean motion tables as they occur in Ptolemaic astronomy. Versions of these programs that also run under Windows 7 and later will soon be made available on this website and/or the website of the project Ptolemaeus Arabus et Latinus.

During a stay at the Institute for History of Science in Frankfurt am Main (Germany) in 1997/1998 I developed a computer database of parameter values occurring in medieval Islamic astronomical texts and tables. This database relies heavily on the hand-written parameter file of Prof. E.S. Kennedy. It includes parameter values directly quoted in primary and secondary sources, as well as values “squeezed” or otherwise estimated from tables.

Useful Links

Nostalgic Links

Most recent modification: 12 October 2022.


Benno van Dalen

Islamic Astronomy

Family History